Add a layer to store Pattern related information

Some information of `canvas_data::Pattern` was lost by
converting it to `raqote::Source` due to the fact that Raqote
did not store this information (e.g. linear gradient's start/end
points). We introduce another layer to keep this information for later
use (like in `is_zero_size_gradient()`).

components/canvas/canvas_data.rs

@@ -358,15 +358,7 @@ pub enum Pattern<'a> {
     #[cfg(feature = "canvas2d-azure")]
     Azure(azure::azure_hl::Pattern, PhantomData<&'a ()>),
     #[cfg(feature = "canvas2d-raqote")]
-    Raqote(raqote::Source<'a>, Option<Repetition>),
-}
-
-#[derive(Clone)]
-pub enum Repetition {
-    Repeat,
-    RepeatX,
-    RepeatY,
-    NoRepeat,
+    Raqote(crate::raqote_backend::Pattern<'a>),
 }
 
 pub enum DrawSurfaceOptions {